This invention relates to a method of automatically forming configuration data for a remainder (described later) which is created in the workpiece because of the edge configuration of the cutting machining tool in a CNC (Computer Numerical Control) machining apparatus.
One example of a machine tool using a CNC unit is a conventional CNC lathe. The CNC lathe receives data on the finally machined configuration (hereinafter referred to as "a final configuration", when applicable) of a work piece to be machined and data on the edge configuration of a cutting tool, to automatically form a machining path for the cutting tool, thereby to machine the workpiece.
FIG. 1 is an explanatory diagram showing the arrangement of the conventional CNC lathe. In FIG. 1, reference numeral 1 designates a CNC. The CNC comprises; a CPU (central processing unit) 2; a memory 3 in which control programs and machining programs have been stored; a keyboard forming input/output means; a CRT (cathode ray tube) 5; and servo drive means including an axial movement control section and a servo amplifier. Further in FIG. 1, reference numeral 7 designates a lathe under the control of the CNC. The lathe comprises: a chuck 9 for holding a work piece 8; a spindle motor for rotating the work piece 8 through the chuck 9; a cutting tool 11 for machining the work piece 8; a tool holder 12 for holding the cutting tool 11; and two servo motors (not shown) which, under the control of the above-described servo drive means 6, move the cutting tool 11 in the direction of the axis of rotation of the work piece 8; i.e., in the direction of X-axis, and in the direction perpendicular to the direction of X-axis; i.e., in the direction of Z-axis through the tool holder 12, respectively.
The operation of the CNC lathe thus organized will be described.
The CPU 2 accesses a control program stored in the memory 3 and processes the commands one by one. Furthermore the CPU 2 accesses a machining program stored in the memory 3 according to the control program, and, according to the machining program, calculates the distance of movement of the cutting tool 11 in the X-Z coordinate plane and applies the distance of movement thus calculated to the servo drive means 6, and pulse-controls the two servo motors (not shown) of the lathe 7 with the aid of the servo drive means 6, to machine the work-piece 8. That is, according to the final configuration data of the workpiece 8 and the edge configuration data of the cutting tool 11 which have been inputted through the keyboard 4 according to the machining program mentioned above, the workpiece 8 is machined to the edge-corrected configuration which is determined by taking the tool angle into account. For instance, as shown in FIG. 2, a train of final configuration data blocks p.sub.0 through P.sub.3 are inputted, with which the final configuration section of a cylindrical workpiece 8 (taken along the central axis) is defined by connecting the points p.sub.0, p.sub.1, p.sub.2 and p.sub.3. Then a train of edge-corrected configuration data blocks p.sub.0, q.sub.0, p.sub.2 and p.sub.3, with which, similarly, the section is defined by connecting the points p.sub.0, q.sub.0, p.sub.2 and p.sub.3, are formed in the memory 3. According to the train of edge correct configuration data blocks thus formed, a machining path is automatically formed for the cutting tool 11, so that the workpiece 8 is machined.
However, in this operation, as is apparent from the above-described final configuration an annular portion p.sub.0 -p.sub.1 -q.sub.0 triangular in section remains unmachined (hereinafter referred to as "a remainder", when applicable). Therefore, the configuration data of the remainder are obtained, for instance, by calculation, and inputted through the keyboard 4 in advance, and as shown in FIG. 3 a cutting tool 11a whose edge is orientated opposite to the edge of the cutting tool used for the machining of the edge-corrected configuration is moved in the opposite direction so that the remainder of the workpiece 8 is machined.
In a CNC machine tool such as the above-described conventional CNC lathe, in order to remove the remainder which is formed because of the configuration of the edge of the cutting tool 11, it is necessary to form the configuration data of the remainder separately and to input them in advance. This is considerably troublesome in the operation.